Dual-Walled Coiled Tubing Deployed Pump

ABSTRACT

Dual-walled coiled tubing assemblies are used to dispose an electric device, such as an electric submersible pump into a wellbore. Dual-walled coiled tubing assemblies include an inner coiled tubing string and an outer coiled tubing string as well as a power cable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the use of strings of coiled tubingto dispose devices, such as electrical submersible pumps into awellbore.

2. Description of the Related Art

Electric submersible pumps (ESPs) are used to pump hydrocarbon fluidsand/or water from subterranean locations. ESPs require electrical powerto be supplied to them from surface. A typical ESP assembly includes acentrifugal pump that is mounted to an electrical motor. A power cableextends from the surface to the motor of the ESP assembly.Conventionally, when ESPs are run into a wellbore, the power cable isstrapped to the outer surface of production tubing sections.

SUMMARY OF THE INVENTION

The invention provides systems and methods for disposing an ESP, orsimilar device, into a wellbore using running arrangements whichincorporate inner and outer coiled tubing strings as well as a powercable which provides power to the motor of the ESP. In a first describedembodiment, a power cable is disposed radially between inner and outercoiled tubing strings. In a second described embodiment, a power cableis disposed within the inner coiled tubing string. These runningarrangements provide flow paths which allow for the flow of producedfluids. In certain embodiments, two flow paths are provided.

The use of dual-walled coiled tubing string running assemblies providesthe possibility of injecting an ESP into a live well which has pressureat surface. Depending upon the corrosiveness of the wellbore environmentand the cable location (i.e., within the inner coiled tubing string orbetween the inner and outer coiled tubing strings), tubing of differentgrades, including Cr16, could be used. With the proper selection ofcoiled tubing and ESP components, arrangements constructed in accordancewith the present invention provide the potential to run an ESP assemblydeeper into a well than conventional technologies permit.

Production arrangements are described which use dual-walled coiledtubing run ESPs to produce hydrocarbon production fluids from wellbores.Embodiments are described wherein capillary lines are located within thedual-walled coiled tubing assembly. The invention encompassesdual-walled coiled tubing assemblies that are used to dispose anelectric device (such as an ESP) into a wellbore. Additionally, theinvention encompasses hydrocarbon production assemblies that include anESP as well as a dual-walled coiled tubing assembly that is used todispose the ESP into a wellbore.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and further aspects of the invention will be readilyappreciated by those of ordinary skill in the art as the same becomesbetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings in whichlike reference characters designate like or similar elements throughoutthe several figures of the drawing and wherein:

FIG. 1 is a side, cross-sectional view of an exemplary wellbore withinwhich is disposed a dual-walled coiled tubing running arrangement and anESP assembly in accordance with the present invention.

FIG. 1a is a side, cross-sectional view of a wellbore within which isdisposed an alternative dual-walled coiled tubing running arrangementand ESP assembly.

FIG. 1b is a side, cross-sectional view of a wellbore within which isdisposed a further alternative dual-walled coiled tubing runningarrangement and ESP assembly.

FIG. 2 is a side, cross-sectional view of a first embodiment for adual-walled coiled tubing running arrangement which might be used withthe ESP assembly shown in FIG. 1, 1 a or 1 b.

FIG. 2a is a side, cross-sectional view of a modified first embodimentfor a dual-walled coiled tubing running arrangement wherein the innercoiled tubing string and power cable are twisted to form a spiralconfiguration.

FIG. 2b is a side, cross-sectional view of a further modified embodimentfor a dual-walled coiled tubing running arrangement wherein the innercoiled tubing string and power cable are twisted to form a spiralconfiguration.

FIG. 3 is an axial cross-section taken along lines 3-3 in FIG. 2.

FIG. 4 is a side, cross-sectional view of an alternative embodiment fora dual-walled coiled tubing running arrangement which might be used withthe ESP assembly shown in FIG. 1.

FIG. 5 is an axial cross-section taken along lines 5-5 in FIG. 4.

FIG. 6 is a side, cross-sectional view of the lower end of a hydrocarbonproduction assembly being used to produce gas-impregnated productionfluid.

FIG. 7 is an axial cross-sectional view of a dual-walled coiled tubingassembly containing capillary lines in a first exemplary arrangement.

FIG. 8 is an axial cross-sectional view of an exemplary dual-walledcoiled tubing assembly containing capillary lines in a second exemplaryarrangement.

FIG. 9 is an axial cross-sectional view of an exemplary dual-walledcoiled tubing assembly containing capillary lines in a third exemplaryarrangement.

FIG. 10 is an axial cross-sectional view of an exemplary dual-walledcoiled tubing assembly containing capillary lines in a fourth exemplaryarrangement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term “dual-walled,” as used herein, is intended to refer broadly toarrangements wherein an inner tubular string or member is locatedradially within an outer tubular string or member to provide adual-walled tubing structure. A structure can be dual-walled withoutregard to whether the inner and outer tubular strings are coaxial orconcentric.

FIG. 1 depicts an exemplary wellbore 10 that has been drilled throughthe earth 12 from the surface 14 down to a hydrocarbon-bearing formation16. It is desired to pump hydrocarbon fluids from the formation 16 tothe surface 14. It is noted that, while wellbore 10 is illustrated as asubstantially vertical wellbore, it might, in practice, have portionsthat are inclined or horizontally-oriented. The wellbore 10 is linedwith metallic casing 18 in a manner known in the art.

In the arrangement shown in FIG. 1, an electric submersible pump (ESP)assembly 20 is disposed within the wellbore 10 having been run in by acoiled tubing running arrangement 22. There is no downhole packer. TheESP assembly 20 includes a motor 24 and a fluid pump 26 which is poweredby the motor 24. In operation, production fluid is drawn into fluidinlets 27 of the pump 26 and exits via the top of the pump 26 into thecoiled tubing running arrangement 22. Conduit 28 transmits electricalpower past the pump 26 and to the motor 24. The ESP assembly 20 mightalso incorporate a seal section or other components as is known in theart.

According to a second exemplary arrangement, which is depicted in FIG.1a , an ESP assembly 20 is disposed within wellbore 10 below a downholepacker 70 and having been run in by a coiled tubing running arrangement22. The ESP assembly 20 includes a motor 24 and a fluid pump 26 which ispowered by the motor 24. In operation, production fluid is drawn intofluid inlets 27 of the pump 26 and exits via the top of the pump intothe running arrangement 22 or into the casing annulus 29, or both, asillustrated by arrows 25. The electrical conduit 28 transmits electricalpower through the packer 70 past the pump 26 and to the motor 24.Conduit 28 may contain hydraulic lines and or instrumentation lines aswell as the electrical cable powering the motor 24. The ESP assembly 20might also incorporate a seal section or other components as is known inthe art.

FIG. 1b depicts a third exemplary arrangement which includes a downholepacker 70. An ESP assembly 20 is disposed within the wellbore 10 abovethe downhole packer 70, having been run in by a dual-walled coiledtubing assembly 22. The ESP assembly 20 includes a motor 24 and a fluidpump 26 which is powered by the motor 24. In operation, production fluidis drawn into the bottom of the packer 70, from there into the bottom ofpump 26 and exits via the top of the pump 26 into the annulus 29. Inthis example, the motor 24 is located above the pump 26. Electricalpower is supplied to the motor 24 directly via the dual-walled coiledtubing assembly 22. The ESP assembly 20 might also incorporate a sealsection or other components as is known in the art. It is noted thatthere may be other arrangements depicting different locations of themotor 24 relative to the pump 26 and either of these relative to thepacker 70. It is also noted that there may be additional combinations ofproduction flow paths available within or outside the dual-walled coiledtubing assembly 22.

FIGS. 2 and 3 illustrate a first embodiment for a dual-walled coiledtubing assembly 30 which might be used for the coiled tubing runningarrangement 22. The dual-walled coiled tubing assembly 30 includes aninner coiled tubing string 32 and an outer coiled tubing string 34 whichradially surrounds the inner coiled tubing string 32. The inner coiledtubing string 32 defines an inner coiled tubing central axial passage 36along its length. The outer coiled tubing string 34 also defines anouter coiled tubing central axial passage 38 along its length. Exemplarysizes for the inner and outer coiled tubing strings 32, 34 would be:1.25″ O.D.×0.125″ wall thickness for the inner coiled tubing string 32and 2.375″ O.D.×0.156″ wall thickness for the outer coiled tubing string34. However, these dimensions are exemplary only, and other sizes anddimensions might be used. The inner and outer coiled tubing strings 32,34 are normally connected together mechanically at surface and downholeends and both would be hung off from the wellhead. Therefore, bothstrings 32, 34 may aid in supporting the weight of the ESP assembly 20as well as the inner and outer coiled tubing strings 32, 34 and powercable 40.

A power cable 40 is disposed radially between the inner and outer coiledtubing strings 32 and 34. The depicted power cable 40 has threeelectrical conductors 42 contained within an insulating sheath 44. Thepower cable 40 may contain other elements, such as a gas barrier, ajacket or armor, as generally known in the art. Although three powerconductors 42 are depicted and are typical, there may be more or fewerthan three depending upon the requirements for downhole power andcontrol. Referring to FIG. 3, it can be seen that the power cable 40preferably has a generally kidney-shaped or oblong, curvedcross-sectional area. This cross-sectional shape permits the cable 40 tofit between the inner and outer coiled tubing strings 32, 34. The sidesurface 41 of the cable 40 which abuts the inner coiled tubing string 32is concave and curved in a manner to be generally complementary to theouter surface of the inner coiled tubing string 32. The opposite sidesurface 43 of the cable 40 is convex and curved in a manner to begenerally complementary to the inner surface of the outer coiled tubingstring 34. It should be noted that the cable 40 need not necessarilyhave a kidney shape, but may, if desired, be round, rectangular or haveother cross-sectional shapes. The cable 40 may be built flat orinstalled flat to bend somewhat during installation to substantiallymatch the outer contour of the inner coiled tubing string 32.Alternatively, the cable 40 may become bent into a curved or kidneyshape due to the clamping forces of straps 46. Friction between thecable 40/inner coiled tubing string 32 and the outer coiled tubingstring 34 will help transmit a portion of the weight of the cable 40 andESP assembly 20 to the outer coiled tubing string 34.

Flexible straps 46 are used to secure the cable 40 to the inner coiledtubing string 32. The term “strap” is used here to denote any form oftensile or compressive fastener, such as a cable, rope, tie, binder,clamp and the like. The straps 46 may be secured about the cable 40 andinner coiled tubing string 32 by tightening, tying, latching, bolting orin other ways known in the art. The straps 46 enclose both the cable 40and inner coiled tubing string 32. When the dual-walled coiled tubingassembly 30 is assembled, an axial fluid flowpath 48 is defined withinthe outer coiled tubing string 34. In the depicted assembly 30, thecentral axial passage 36 provides a first axial fluid flowpath while theaxial fluid flowpath 48 serves a second axial fluid flowpath. Thepresence of two, separate axial fluid flowpaths within a single assembly30 provides the advantage of allowing two separate streams of fluid tobe transmitted along the assembly 30. Fluids might be transmitted upholeas a result of the ESP pump 26 or transmitted downhole in instanceswherein one of the flow paths is being used to inject specializedfluids, which might include scale or asphaltene inhibitors.

It is noted that the inner coiled tubing string 32 is shown as offsetfrom the center of the outer coiled tubing string 34 due to the presenceof the cable 40. As illustrated in FIG. 2a , the cable 40 and innercoiled tubing string 32 are preferably twisted along their length toprovide a spiral configuration. An alternative embodiment is depicted inFIG. 2b wherein the cable 40 is spiraled around the inner coiled tubingstring 32. The inventors have determined that these spiralconfigurations are desirable since they distribute the stresses on thecable 40 more uniformly as the dual-walled coiled tubing assembly 30 isspooled onto and off of a reel. It should be appreciated that, inalternative embodiments, the coiled tubing strings 32, 34 may bearranged concentrically rather than having offset centers.

The dual-walled coiled tubing assembly 30 may be assembled by firstdisposing the cable 40 in parallel contact with the inner coiled tubingstring 32 and then affixing the cable 40 to the inner coiled tubingstring 32 with straps 42. Preferably, the straps 42 are used to affixthe cable 40 to the inner coiled tubing string 32 in appropriate spacedintervals which are sufficient to affix the cable 40 to the inner coiledtubing string 32 without permitting a large degree of sagging of thecable 40 and to ensure that the cable weight is held uniformly by theinner coiled tubing string 32 in order to prevent breakage of the cable40. Thereafter, the inner coiled tubing string 32 and affixed cable 40are disposed into the outer coiled tubing string 34. This may be donevertically while the outer coiled tubing string 34 is hanging in a well.Alternatively, it may be done horizontally with the outer coiled tubingstring 34 stretched out and with the inner coiled tubing string 32 andaffixed cable 40 either pushed or pulled into the outer coiled tubingstring 34. Metal-to-metal lubricants can be used to reduce the contactfriction and ease the installation. More typically, the cable 40 can befastened to the inner coiled tubing string 32 as the inner coiled tubingstring 32 is disposed into the outer coiled tubing string 34. As thecable 40 is affixed to the inner coiled tubing string 32, both aredisposed into the outer coiled tubing string 34. This may be donevertically as the outer coiled tubing string 34 is hanging in a well.Alternatively, it may be done horizontally with the outer coiled tubingstring 34 stretched out and with the inner coiled tubing string 32either pushed or pulled into the outer coiled tubing string 34, takingthe cable 40 along with it. Again, metal-to-metal lubricants can be usedto reduce the contact friction and ease installation.

An assembled dual-walled coiled tubing assembly 30 can be wound onto acoiled tubing reel of a type known in the art for retaining spools ofcoiled tubing and transported to a well site for use. An ESP assembly,such as ESP assembly 20 is then affixed to the coiled tubing assembly 30and run into the wellbore in conventional fashion.

A further method of injecting cable through a coiled tubing string wouldbe to use a water-based metal-on-metal lubricant with a low coefficientof friction, such as EasyReach™ lubricant, that will permit longerlengths of cables and coiled tubing strings to be disposed withinsurrounding coiled tubing strings. Modeling of these lengths could beperformed taking into account coiled tubing sizes and cable sizes andusing suitable software designed for design and planning for coiledtubing operations.

FIGS. 4-5 illustrate an alternative embodiment for a dual-walled coiledtubing assembly 50 which might be used for the coiled tubing runningarrangement 22. The dual-walled coiled tubing assembly 50 includes aninner coiled tubing string 32 and an outer coiled tubing string 34.Power cable 40′ is disposed within the central axial passage 36 of theinner coiled tubing string 32. Power cable 40′ preferably has a circularcross-section and is shaped and sized to fit tightly within the centralaxial passage 36 of the inner coiled tubing string 32. To the extentthat there is a radial gap 51 between the power cable 40′ and the innercoiled tubing string 32, this gap 51 may be used as a second andseparate flow path to transmit fluid through the dual-walled coiledtubing assembly 50. Alternatively, power cable 40′ may have anon-circular cross-section or may not fit tightly within the centralaxial passage 36 of the inner coiled tubing string 32. The power cable40′ may fit loosely and rely upon the contact friction of its spiraledshape within the inner coiled tubing string 32 to support its weight.Also, the power cable 40′ may fit loosely and be supported at regularintervals by support clamps attached to the cable 40′. In thesesituations, there could be fluid flow past the cable 40′.

The dual-walled coiled tubing assembly 50 may be assembled by firstdisposing the cable 40′ into the central axial passage 36 of the innercoiled tubing string 32. This may be done vertically by lowering thecable 40′ into the inner coiled tubing string 32 while it is hangingvertically in a well. Alternatively, it may be done horizontally withthe inner coiled tubing string 32 stretched out and with the cable 40′pulled into the inner coiled tubing string 32. Once more, metal-to-metallubricants can be used to reduce the contact friction and easeinstallation. The cable 40′ may also be placed into the inner coiledtubing string 32 while the inner coiled tubing string 32 is beingmanufactured. The inner coiled tubing string 32 and cable 40′ are theninserted into the outer coiled tubing string 34. These two previoussteps may be reversed. An assembled dual-walled coiled tubing assembly50 can be wound onto a coiled tubing reel of a type known in the art forretaining spools of coiled tubing and transported to a well site foruse. An ESP assembly, such as ESP assembly 20 is then affixed to thecoiled tubing assembly 50 and run into the wellbore 10.

The inventors believe that dual-walled coiled tubing assembliesconstructed in accordance with the present invention are advantageousfor running ESPs into wellbores. The cable 40 is protected from damagesince it is contained within the protection of the outer coiled tubingstring 34. Such damage has been known to occur as a result of wellboredebris or disposal of the cable through deviated or horizontal wellboreportions. In some constructions, dual fluid flowpaths are available forflow of fluid along the assembly. Additionally, disposing the cablewithin the outer coiled tubing string 34 permits a standard packer to beset in the wellbore without the need for a specialized arrangementhaving a bypass to allow a separate cable to be disposed through thepacker. The various fluid flowpaths provided by the dual-walled coiledtubing assemblies (i.e., 30, 50) of the present invention might alsoprovide one or more pressurized paths for use in downhole activationschemes in which a port is opened or closed or a tool, such as a packeris activated.

FIG. 6 illustrates an exemplary production arrangement whichincorporates a dual-walled coiled tubing assembly in accordance with thepresent invention and which is being used to produce gas-impregnatedproduction fluid. A production assembly 60 includes dual-walled coiledtubing assembly 30 wherein dual fluid flowpaths are provided. An ESPassembly 20 is affixed to the dual-walled coiled tubing assembly 30 andincludes a motor section 24, pump section 26 and a gas separator section29 of a type known in the art. First and second bypass conduits 62 and64 extend from the gas separator section 29 past the motor section 24and enter the dual-walled coiled tubing assembly 30. The bypass conduits62, 64 are shown in FIG. 6 to be located external to the ESP assembly 20but may, more typically, be located internally within the ESP assembly20. During operation, the gas separator section 29 separates gas fromthe raw feed of gas-impregnated hydrocarbon production fluid. Inparticular, flow (indicated by arrow 66) from the first bypass conduit62 is directed into axial fluid flowpath 48. The remaining hydrocarbonproduction fluid is directed through second bypass conduit 64 (arrow 68)into axial fluid flowpath 36. The dual-walled coiled tubing assembly 30is shown passing through a packer 70. Because in this example the powercable 40 is retained within the outer coiled tubing string 34, aconventional packer 70 may be used without the need for a device thatallows for a separate pass-through for the cable 40.

An arrangement which the inventors believe would be desirable forcertain production situations would be an arrangement similar to thatdepicted in FIG. 1 with hydrocarbon flow up one flow path. A secondarrangement which the inventors believe would be desirable for certainproduction situations would be an arrangement similar to that shown inFIG. 1a with fluid flow going up one flow path and with the outer coilcasing annulus isolated by the packer 70. Both of these arrangementsbecome possible for installation into live wells due to the ability toseal around the outer coiled tubing string 34 using conventional coiledtubing running equipment. This removes the possibility of well damageresulting from having to kill the well during conventional tubinginstallation. The inventors believe that using dual-walled coiled tubingassemblies with conventional equipment improves the speed ofinstallation of the ESP as opposed to conventional tubing, therebyminimizing down time, lost production time and reducing cost.

FIGS. 7, 8 and 9 illustrate exemplary placements for capillary lineswithin dual-walled coiled tubing assemblies in accordance with thepresent invention. Capillary lines may be used to provide hydraulicmotive force to actuate valves or to inflate or release certainhydraulic downhole equipment. Alternatively, capillary lines can be usedto provide conduits to inject specialized fluids into the dual-walledtubing assembly 30 or 50 at depth. These specialized fluids may includescale or asphaltene inhibitors. In further embodiments, capillary linesare instrumentation lines which can, for example, be used to monitordownhole temperatures or pressures among other downhole parameters. Infurther embodiments, high strength steel cables (or other material) canbe installed within the ESP bundle, their purpose being to carry some ofthe ESP cable weight. In each described embodiment, capillary lines areretained radially inside of the outer coiled tubing string, therebyproviding protection from damage for the capillary lines.

FIG. 7 depicts a first exemplary dual-walled coiled tubing assembly 72which is similar in most respects to the dual-walled coiled tubingassembly 30 described previously. The dual-walled coiled tubing assembly72 includes an inner coiled tubing string 32 and an outer coiled tubingstring 34 as well as power cable 40. Capillary lines 74 are disposedwithin the outer coiled tubing central axial pathway 38 alongside theinner coiled tubing string 32 and the cable 40. Straps 46 secure thecable 40 and the capillary lines 74 to the inner coiled tubing string32.

FIG. 8 illustrates an alternative exemplary dual-walled coiled tubingassembly 76. The dual-walled coiled tubing assembly 76 includes an innercoiled tubing string 32 and an outer coiled tubing string 34 as well aspower cable 40 a. Capillary lines 74 are disposed within the power cable40 a alongside the conductors 42.

FIG. 9 depicts a further alternative exemplary dual-walled coiled tubingassembly 78 in accordance with the present invention. The dual-walledcoiled tubing assembly 78 is similar in many respects to the dual-walledcoiled tubing assembly 50 described previously. The dual-walled coiledtubing assembly 78 includes inner coiled tubing string 32 and an outercoiled tubing string 34. Power cable 40′ is disposed within the innercoiled tubing string central axial passage 36. Capillary lines 74 aredisposed radially between inner coiled tubing string 32 and outer coiledtubing string 34. Straps 46 secure the capillary lines 74 to the innercoiled tubing string 32. A fluid flow path 48 defined within thedual-walled coiled tubing assembly 78.

FIG. 10 depicts a further alternative exemplary dual-walled coiledtubing assembly 80 which is similar in many respects to the dual-walledcoiled tubing assembly 50 described previously. The dual-walled coiledtubing assembly 80 includes inner coiled tubing string 32 and outercoiled tubing string 34. Power cable 40′ is disposed within the innercoiled tubing string 32 central axial passage 36. Capillary lines 74 aredisposed within the power cable 40′ alongside the conductor 42. A fluidflow path 48 is defined within the dual-coiled tubing assembly 80. Wherethere are multiple capillary lines 74, at least first and second fluidinjection paths are provided within the outer coiled tubing string 34 bythe multiple capillary lines.

The use of dual-walled coiled tubing assemblies, such as assemblies 30,50 described herein, provide the possibility of injecting an ESPassembly 20 into a live wellbore 10 which is under pressure from surface14. Because the power cable 40140′140 a is contained within the outercoiled tubing string 34, it is mechanically protected from damage due tofriction or abrasion with a surrounding casing or other objects orsurfaces during run-in. ESPs run on standard coiled tubing or on regulartubing, where the power cable is strapped to the outside of the tubing,the ESP assembly cannot normally be run into live wells since there iscurrently not an effective way to seal around the tubing and cableduring running in. Therefore, the pressure at surface cannot becontained. In order to run into a live wellbore, in one embodiment, thesystem would be sealed into a downhole packer and fluid produced up thedual-walled coiled tubing assembly.

Depending upon the corrosiveness of the wellbore environment into whichthe ESP 20 will be run, and the location of the power cable 40 or 40′140a, coiled tubing of different grades, including Cr16 grade stainlesssteel, could be used. For example, depending upon downhole conditions,the inner and outer coiled tubing strings 32, 34 may be made ofdifferent grades of steel, thereby maximizing their resistance tocorrosion.

The foregoing description is directed to particular embodiments of thepresent invention for the purpose of illustration and explanation. Itwill be apparent, however, to one skilled in the art that manymodifications and changes to the embodiment set forth above are possiblewithout departing from the scope and the spirit of the invention.

What is claimed is:
 1. A dual-walled coiled tubing assembly to disposean electric submersible pump into a wellbore, the dual-walled coiledtubing assembly comprising: an inner coiled tubing string defining aninner coiled tubing central axial pathway along its length; an outercoiled tubing string radially surrounding the inner coiled tubingstring, the outer coiled tubing string defining an outer coiled tubingstring central axial passage along its length; and a power cable toprovide electric power to the electric device, the power cable beingdisposed within the outer coiled tubing string central axial passage. 2.The dual-walled coiled tubing assembly of claim 1 wherein the powercable is further disposed within the inner coiled tubing central axialpassageway.
 3. The dual-walled coiled tubing assembly of claim 1 whereinthe power cable is disposed radially between the inner coiled tubingstring and the outer coiled tubing string.
 4. The dual-walled coiledtubing assembly of claim 1 further comprising one or more capillarylines disposed within the outer coiled tubing string.
 5. The dual-walledcoiled tubing assembly of claim 4 wherein the one or more capillarylines is/are located radially between the inner coiled tubing string andthe outer coiled tubing string.
 6. The dual-walled coiled tubingassembly of claim 4 wherein the one or more capillary lines is/arelocated radially within the inner coiled tubing string.
 7. Thedual-walled coiled tubing assembly of claim 4 wherein the one or morecapillary lines is/are located within the power cable.
 8. Thedual-walled coiled tubing assembly of claim 1 further comprisingseparate first and second fluid flow paths defined within the outercoiled tubing string.
 9. The dual-walled coiled tubing assembly of claim1 further comprising at least one strap securing the power cable to theinner coiled tubing string.
 10. The dual-walled coiled tubing assemblyof claim 1 wherein the electric submersible pump assembly includes apump section and a motor section.
 11. The dual-walled coiled tubingassembly of claim 1 wherein the power cable presents an axialcross-section having: a first side surface that is concave and shaped tobe generally complementary to an outer radial surface of the innercoiled tubing string; and a second side surface that is convex andshaped to be generally complementary to an inner radial surface of theouter coiled tubing string.
 12. A hydrocarbon production assembly toproduce hydrocarbon fluid from a wellbore, the production assemblycomprising: an electric submersible pump; a dual-walled coiled tubingassembly to dispose the electric submersible pump into the wellbore, thedual-walled coiled tubing assembly comprising: an inner coiled tubingstring defining an inner coiled tubing central axial pathway along itslength; an outer coiled tubing string radially surrounding the innercoiled tubing string, the outer coiled tubing string defining an outercoiled tubing string central axial passage along its length; and a powercable to provide electric power to the electric submersible pump, thepower cable being disposed within the outer coiled tubing string centralaxial passage.
 13. The hydrocarbon production assembly of claim 12wherein the power cable is further disposed within the inner coiledtubing central axial passageway.
 14. The hydrocarbon production assemblyof claim 12 wherein the power cable is disposed radially between theinner coiled tubing string and the outer coiled tubing string.
 15. Thehydrocarbon production assembly of claim 12 further comprising one ormore capillary lines disposed within the outer coiled tubing string. 16.The hydrocarbon production assembly of claim 15 wherein the one or morecapillary lines is/are located radially between the inner coiled tubingstring and the outer coiled tubing string.
 17. The hydrocarbonproduction assembly of claim 15 wherein the one or more capillary linesis/are located within the power cable.
 18. The hydrocarbon productionassembly of claim 12 further comprising separate first and second fluidflowpaths defined within the outer coiled tubing string.
 19. Thehydrocarbon production assembly of claim 12 further comprising at leastone strap securing the power cable to the inner coiled tubing string.20. The hydrocarbon production assembly of claim 12 wherein the powercable presents an axial cross-section having: a first side surface thatis concave and shaped to be generally complementary to an outer radialsurface of the inner coiled tubing string; and a second side surfacethat is convex and shaped to be generally complementary to an innerradial surface of the outer coiled tubing string.
 21. The hydrocarbonproduction assembly of claim 12 further comprising a packer forming aseal between the dual-walled coiled tubing assembly and the wellbore andwherein: an annulus is defined between the dual-walled coiled tubingassembly and the wellbore; and production fluid is flowed through theannulus.
 22. The hydrocarbon production assembly of claim 12 furthercomprising a packer forming a seal between the dual-walled coiled tubingassembly and the wellbore and wherein: an annulus is defined between thedual-walled coiled tubing assembly and the wellbore; and productionfluid is flowed through the dual-walled coiled tubing assembly.
 23. Thehydrocarbon production assembly of claim 12 further comprising a packerforming a seal between the dual-walled coiled tubing assembly and thewellbore and wherein: an annulus is defined between the dual-walledcoiled tubing assembly and the wellbore; and production fluid is flowedthrough the annulus and the dual-walled coiled tubing assembly.
 24. Thedual-walled coiled tubing assembly of claim 12 further comprisingseparate first and second fluid injection paths defined within the outercoiled tubing string.
 25. The dual-walled coiled tubing assembly ofclaim 12 wherein at least one of the inner and outer coiled tubingstrings are formed of corrosion-resistant material and one of the innerand outer coiled tubing strings is composed of a grade of metal that isdifferent from that of the other of the inner and outer coiled tubingstrings.
 26. The dual-walled coiled tubing assembly of claim 12 whereina metal-to-metal lubricant is used during manufacture of the dual-walledcoiled tubing assembly.